| 摘要 |
PROBLEM TO BE SOLVED: To provide an active control type noise reducing device which can obtain excellent sound reduction effect over a wide frequency range. SOLUTION: An M-series signal sound is radiated by a dummy sound source 18 which is arranged nearby a noise source S. A control point microphone 25 is arranged at a control point C nearby the upper side of a soundproofing barrier 10 and a computer 26 computes a filter coefficient for reducing the M-series signal sound according to the output of the microphone and sets it. A filter performs a digital filtering process by using the digital value of the output of a sound source microphone 20 arranged nearby a dummy sound source 18 and the set filter coefficient and according to the filter output, a control speaker 14 radiates a control sound for reducing noise.
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